The invention relates to the control of stepper motors, which are found for example in motor vehicle dashboards for driving needle-type indicators.
Broadly, a stepper motor comprises a stator, with two coils having orthogonal respective axes giving rise to two orthogonal magnetic fields, and a polarized rotor aligned along the resultant of the two stator fields. In order to turn the rotor and hence the magnetic resultant, the energy supplies to the two coils of the stator are made to vary. It is known practice to energize these coils from a micro-controller with differential PWM (pulse width modulation) outputs; a coil being energized through a pair of conductors, it is possible to control the sense of the difference in potentials at the two terminals of the coils so as to drive the vector of the magnetic resultant into one or other of the four quadrants of the trigonometric circle which are defined, as may be recalled, by the sine and the cosine of the angle xcex8 of the resultant vector with the positive reference half-axis:
Since there is often a plurality of stepper motors in an item of equipment, the micro-controllers found on the market are those having differential PWM outputs capable of controlling several motors. This often results in the drawback of having a micro-controller which is either over-engineered or under-engineered and, in this case, with the additional drawback of having to provide one or more additional components to control the surplus motors.
The present invention aims to alleviate these drawbacks and to dispense with the expensive micro-controllers having differential PWM outputs.
Accordingly, it relates to a generator having at least two pairs of differential PWM outputs, characterized in that it comprises
i) a microprocessor having at least one normal PWM output,
ii) two assemblies, each having at least two outputs and linked by an input to the normal PWM output of the microprocessor, each assembly being configured so that one of its two outputs corresponds to the PWM output of the microprocessor,
iii) means for inverting the two outputs of each assembly.
Thus, from a simple microprocessor, having a normal PWM output, designed to vary between 0 and 1, stator controls are provided which are able to change sign by virtue of the inverting of the two outputs of each assembly, thus making it possible to select any angle in the four quadrants.
According to a first preferred embodiment, each assembly is configured so that the other of its two outputs remains at an extreme level, for example the higher level, of the PWM output and each assembly is linked, by another input, to an output of the microprocessor for inverting its two outputs.
According to a second preferred embodiment, the microprocessor comprises at least two normal PWM outputs respectively linked to the inputs of the two assemblies, each assembly being configured so that its two outputs are inverted.